"When a decision is made to offer a patient a blood transfusion, the importance of having blood readily available should never be underestimated," consultant haematologist Dr Susan Robinson.

"Donated blood saves lives every day. We are so grateful to the people who donate blood.

"For many of our patients, whether they are receiving blood alongside cancer treatment or because they are bleeding, it is the best gift they can receive."

One of the pioneers of blood transfusion, Dr James Blundell, practised at Guy's Hospital in the 19th century. His first recorded success was treating a woman who had lost blood giving birth. After receiving a few ounces of blood from her husband, the woman survived.

Mike Stredder, director of blood donation at NHS Blood and Transplant, the service that collects, tests and processes blood for hospitals across England, said: "Blood donation is an amazing gift and we are really grateful to Guy's and St Thomas' NHS Foundation Trust for their support. Blood transfusions save lives and we need people to register as new donors at www.blood.co.uk

"Thanks to the generosity of our current donors, hospitals have the blood needed to treat patients and there is not a crisis in blood stocks. Despite overall blood use in hospitals declining, we need more people to start giving blood to replace those who can no longer donate and to ensure we have the right mix of blood groups to match patient needs in the future.

"We need more young donors to help ensure the future of blood donation. We also particularly need more people of Black African, Black Caribbean, mixed race, Arab and South Asian heritage to become blood donors to reflect the ethnic diversity of patients.

"Don't worry if you've never given blood before and don't know what blood group you are – you find out shortly after your first donation. What's important is that you register as a donor and book your first appointment to donate."